It is known to use block copolymers that have a hydrophilic polymer chain segment and a hydrophobic polymer chain segment as a carrier for drugs and it is also known to encapsulate a predetermined drug into a polymer micelle formed of such block copolymers (for example, Patent Document 1 or 2). A composition containing a homogeneous polymer micelle encapsulating a poorly water-soluble drug and a preparation method therefor are also known (Patent Document 3).
Patent Documents 1 and 2 each describe a method for encapsulating a drug into a micelle preliminarily formed from block copolymers in an aqueous medium by adding the drug to the micelle solution, and optionally, mixing and stirring the resulting mixture under heating and ultrasonication. Further, Patent Document 3 describes a method for preparing a polymer micelle encapsulating a drug by dissolving block copolymers and drugs in a water-miscible polar solvent and then subjecting the resulting mixture to dialysis against water.
According to these prior art references, it is understood that the use of the polymer micelle as a carrier for drugs has various advantages including a sustained release of the drug. However, in conventional polymer micelles, the drug is encapsulated into the micelle in a very stable manner, which may inhibit the drug from being released in a suitable manner.